The invention relates to the field of antiviral agents, and more specifically to antiviral therapy.
One of the great paradoxes of medicine is that the simplest of organisms are the most difficult to control. While great progress has been made in controlling more complex organisms, with hundreds of different antibacterial pharmaceutical compositions or antibiotics, there are very few pharmaceutical compositions intended or adapted for antiviral therapy that are of proven effectiveness. The major drawback in developing antiviral agents has been an inability to distinguish viral replicative mechanisms from host replicative processes. Nevertheless, progress has been made over the past two decades in discovering molecules necessary for virus replication, in characterising them mechanistically, and in developing antiviral agents to inhibit them (for review see Hirsch et al., In: Fields Virology, Chapter 15, Lippincot-Raven Publishers, 1996). Well known antiviral agents include amantadine, rimandatine and other anti-influenza agents, acyclovir, gangcyclovir and related agents, foscarnet and other anti-herpesvirus agents, ribavirine and various antiretroviral agents as discussed below.
Progress and understanding in the field of antiretroviral therapy in the past 3 years has been dramatic (for review see Hammer and Yeni. AIDS, 12: S181-S188, 1998). Progress has been fuelled by three major advances. First, increasing knowledge of disease pathogenesis has provided underpinnings for current therapeutic rationale. The proliferative nature of the viral replicative process (1010 virions produced and destroyed each day), the rapid viral turnover (virion plasma half-life of 6 h or less), and the recognition of second and third phases of viral decay under the influence of potent antiretroviral therapy resulting from the presence of longer-lived cell reservoirs has guided the current principles of antiretroviral therapy. The second advance has been the widening array of therapeutic choices represented by the increasing numbers of agents available to patients and clinicians. Finally, the third advance is the availability of increasingly sophisticated patient monitoring techniques, such as viral load determinations that simultaneously provide the tools for dissecting HIV disease pathogenesis and monitoring the effects of treatment in affected individuals. Taken together, these developments have led to the generally accepted principle that potent combination regimens (also called highly active antiviral therapy or HAART) designed to drive and maintain plasma HIV-RNA concentration below the limits of detection of currently available assays are the treatments of choice.
However, a number of practical limitations to this idealised approach have increasingly been recognised. These include: the variability of initial virologic response according to the disease stage, particularly the high rate of failure in those with advanced HIV infection; the challenge of patient adherence to complex regimens; drug failure and the threat of multidrug resistance; the lack of predictably effective salvage therapies; the emergence of longer-term toxicities to the protease inhibitor class of compounds; and the sharpening division between populations of the world related to cost and access to effective agents.
In several countries there are 11 agents approved for the treatment of HIV infection and the reasonable expectation is that the total will rise to 15 shortly (Table 1). These agents are either HIV reverse transcriptase inhibitors of the nucleoside, non-nucleoside, and nucleotide subclasses or members of the HIV-protease inhibitor class. Although the simple calculation of the number of two-, three- and four-drug combinations would suggest that the regimen choices for initial and alternative therapies are vast, in reality they are much more limited as a result of cross-resistance, toxicities, tolerance, drug or food interactions and other practical considerations. Although it is true that the options for initial potent, combination regimens are increasing, when one considers the limitations on subsequent regimens conferred by the initial choice, one realises the restricted options for long-term virologic suppression that currently exist.
In areas where drug access is not a problem, the current recommended standard for initial therapy is a potent in vivo protease inhibitor combined with two nucleoside analogs with the first alternative being a non-nucleoside reverse transcriptease inhibitor in combination with two nucleoside analogs. However, the emergence of drug resistance during treatment and its association with treatment failure have been described with nearly all of the antiretroviral agents in use or in development. Therefore, resistance testing might be thought to logically assist with the choice of alternative treatment in the setting of treatment failure and assist with the choice of initial therapy when primary drug resistance is suspected. However, there are many questions that need to be answered before resistance testing (either genotypic or phenotypic) becomes accepted as a routine clinical tool. In what setting and to what extent this technology will improve decision making is not clear and drug resistance is only one of a number of reasons for treatment failure. Resistance testing results are most reflective of the selective pressure of the current drug that might emerge quickly on a new regimen. Further, one cannot always deduce the phenotypic susceptibility of a viral strain from its genotype because of assay sensitivity and resistance mutational interactions. Cross-resistance, particularly to protease inhibitors, may also be a dynamic process in which viruses are xe2x80x9cprimedxe2x80x9d by mutations selected on a previous therapy to develop resistance more quickly when exposed to a new member of the same drug class.
Failure of a particular antiretroviral drug regimen may be defined clinically, immunologically or virologically. Increasingly, for individuals on their initial drug combination a strict definition of failure is being applied. That is, detectable viremia following previous suppression below the detection limit of the assay are being employed. With the advent of plasma HIV-RNA assays with detection limits at the approximate 50 copies/ml range, this has raised the question of whether a confirmed rise above this threshold should trigger a treatment change given the still limited therapeutic armamentarium.
The advances and the limitations of the currently available antiretroviral agents make it clear that new agents and combinations are urgently needed. On the immediate horizon is the promise of widespread availability of four new agents: abacavir (a nucleoside analog reverse transcriptase inhibitor), efavirenz (a non-nucleoside reverse transcriptase inhibitor), adefovir dipivoxil (a nucleotide reverse transcriptase inhibitor), and amprenavir (a protease inhibitor). These agents will carry with them an increasing number of choices for patients and clinicians but are most likely to benefit antiretroviral-naive or minimally drug-experienced individuals only. Their role in xe2x80x9csalvagexe2x80x9d regimens is currently under investigation but the potential for cross-resistance with the currently approved agents may well limit their effectiveness in this circumstance.
In conclusion, a next wave of drug development is needed that involves new classes of antiviral agents. Other potential anti-viral agents effective against viral targets are needed to broaden the therapeutic possibilities of viral therapy.
The present invention provides use of at least one compound or mixture of compounds of the general formula 
or a functional equivalent or pharmaceutically acceptable salt, ester or hydrate thereof for the production of a pharmaceutical composition for the treatment of a viral infection. Replacements or substitutions of the general formula for example include replacing S with O, Se or Te, and/or additionally substituting the ring with one or more side groups such as R or Rxe2x80x2.
Compounds of the general formula are for example known from Arnoldi et al., J. Chem. Soc., Perkin Trans. 1 (1993), 12:1359-1366; from Poirier et al., Sulfur Lett. (1998) 10:167-173; and from Ohtsuka et al., Chem. Pharm. Bull. (1983) 31:443-453. Furthermore, it is known from Kalgutar et al., Science 280:1268-1270, (1998) and WO 98/29382 that compounds of the general formula covalently inactivate cyclo-oxygenase-2 (COX-2) and are selective inhibitors of prostaglandin endoperoxidase-2 and that a pharmaceutical composition including such compound may be useful for providing pain-relief, such as in the prophylaxis or therapeutic treatment of inflammatory responses such as oedema, fever, algesia, neuromuscular pain, headache, cancer pain or arthritic pain.
Surprisingly, however, it has now found that a pharmaceutical composition including the compound is useful in anti-viral therapy. Not wishing to be bound by theory it is herein assumed that a compound of the general formula or a functional equivalent thereof for example inhibits prostaglandin synthesis by COX-2 and/or binds PPAR-g (peroxisome proliferator-activated receptor-g, a member of the nuclear receptor family of transcription factors) or PPAR-g analogues and therewith antagonises activities of transcription factors such as AP-1, STAT and NF-kB, assumedly with the effect that viral functions such as virus transcription and/or viral gene expression are functionally inhibited, as for example can be detected by testing the effect of such compound on viral promotor activity (see e.g. FIG. 1). Alternatively, the effect on viral protein expression is detected by testing viral protein production in cell culture (see e.g. FIGS. 2, 4a and 4b).